- MAHDHI MosbahTunisian Assistant ProfessorSpeciality: Biological Sciences (Microbiology and Molecular biology)Adress... moreMAHDHI MosbahTunisian Assistant ProfessorSpeciality: Biological Sciences (Microbiology and Molecular biology)Adress: Center for Environmental Research and Studies, Jazan University, Saudi Arabiaedit
Nine isolates from Argyrolobium uniflorum, Lotus creticus, Medicago sativa (Tunisia) and Lotus arabicus (Senegal) were analysed by multilocus sequence analysis (MLSA) of five housekeeping genes (recA, atpD, glnA, gltA and thrC), the 16S... more
Nine isolates from Argyrolobium uniflorum, Lotus creticus, Medicago sativa (Tunisia) and Lotus arabicus (Senegal) were analysed by multilocus sequence analysis (MLSA) of five housekeeping genes (recA, atpD, glnA, gltA and thrC), the 16S rRNA gene and the nodulation gene nodA. Analysis of the individual and concatenated gene sequences demonstrated that the nine new strains constituted three stable, well-supported (bootstrap and gene sequence similarity values) monophyletic clusters, A, B and C, all belonging to the branch of the genus Ensifer, regardless of the phylogenetic reconstruction method used (maximum likelihood, maximum-parsimony, neighbour-joining). The three groups were further characterized by API 100 auxanographic tests, host specificity and nodA gene sequence analysis. On the basis of these data, clusters A and C are suggested as representing two novel species within the genus Ensifer, for which the names Ensifer numidicus sp. nov. (type strain ORS 1407T=LMG 24690T=CIP ...
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ABSTRACT Wild legumes (herbs, shrubs or trees) play a critical role in natural ecosystems, agriculture, and agroforestry, where their ability to fix nitrogen in symbiosis makes them excellent colonizers of low-N environments, and hence an... more
ABSTRACT Wild legumes (herbs, shrubs or trees) play a critical role in natural ecosystems, agriculture, and agroforestry, where their ability to fix nitrogen in symbiosis makes them excellent colonizers of low-N environments, and hence an economic and environmentally friendly species. The field natural nodulation of the wild Tunisian legumes, the genetic diversity and symbiotic-efficiency of their root nodulating bacteria (RNB) and the dynamics of soil fertility under symbiotic association in arid regions of Tunisia were investigated during this study. Natural nodulation varied according to the species and site. Morphologically, nodules were spindle-shaped (Trigonella maritima, Hedysarum spinosissimum, Argyrolobium uniflorum, Genista saharae, Retama reteam, Vicia sativa). The colour of the nodules was not related to that of the roots, but depends on soil quality and colour, and on the presence of leghaemoglobin. Based on molecular techniques (16S rRNA sequencing) and phenotypic characteristics, the root-nodule bacteria isolated from the Tunisian wild legumes were classified into four genera (Rhizobium, Mesorhizobium, Sinorhizobium). No Bradyrhizobium genus was recovered in our results. Non-nodulating bacteria considered as endophytic to nodules were also reported in our results and four genera belonging to Phyllobacterium, Starkeya, Pseudomonas, and Kocuria were taxonomically defined, for Lotus sp. and H. spinosissimum. Bacteria belonging to Sinorhizobium genus were widely distributed in area under study. Wild legumes belonging to Lotus spp., Vicia spp. and Hedysarum spp. were nodulated by this genus. Mesorhizobium genus was restricted to Lotus sp., and Rhizobium genus nodulated Vicia and Lotus. Phenotypically, our results showed that the root nodulating bacteria belonging to the genus Sinorhizobium exhibited higher tolerance to salt stress and elevated temperatures. Based on symbiotic properties, our reports indicated that the wild-legume rhizobia formed effective and successful symbioses with their legume hosts. The diversity and effectiveness of the nitrogen-fixing wild legumes are of major significance to soil fertility dynamics in the arid regions. Effects on enzyme activities, microbial biomass and respiration, were evaluated in different agricultural soils and in the presence of different wild legumes such as G. saharae and R. raetam. Results showed that legumes–rhizobia symbiosis improves enzyme activities, microbial biomass and respiration of field soils and regenerate microbiological properties and the microflora activity involved in the decomposition of organic matter.
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ABSTRACT Thirty-five isolates of rhizobia were picked up fromRetama raetam root nodules growing in arid lands of Tunisia. A genotypic approach including PCR-RFLP of 16S rDNA and 16S–23S rDNA was used to study their diversity and their... more
ABSTRACT Thirty-five isolates of rhizobia were picked up fromRetama raetam root nodules growing in arid lands of Tunisia. A genotypic approach including PCR-RFLP of 16S rDNA and 16S–23S rDNA was used to study their diversity and their relationships with te n reference strains of rhizobia. Four distinct clusters were defined in numerical analysis of RFLP of 16S rDNA, which related at the 78% similarity level to distinct species ofMesorhizobium, Agrobacterium, Rhizobium andSinorhizobium. More greater variability was detected by analysis of Intergenic Spacers 16S–23S rDNA. The results from both methods used in this study, showed that among all newsolates only three were found to be closely related to species of the genusSinorhizobium.
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ABSRACT Fifteen endophytic bacterial isolates associated to root nodules of Vicia sativa growing in arid zone of Tunisia were examined by phenotypic characterization and 16S rDNA analysis. Measured phenotypic characteristics included... more
ABSRACT Fifteen endophytic bacterial isolates associated to root nodules of Vicia sativa growing in arid zone of Tunisia were examined by phenotypic characterization and 16S rDNA analysis. Measured phenotypic characteristics included growth rate, colony morphology, and tolerances to extremes temperature, salt and pH. The isolates were very diverse phenotypically. All isolates were fast-growing rhizobia with generation time of 2-6 hours. The majority of isolates tolerated high concentration of Nacl (2 %), alkaline pH and grew at 37°C. Numerical analysis of PCR-RFLP of 16S rDNA showed that only one isolate (ViB15) was closely related to Sinorhizobium meliloti type species. New isolates grouped separately from reference strains and formed two clusters at 80 % of similarity, which indicates that new isolates were genetically very diverse.
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In the context of climate change, increasing earth population and burst of energy cost, legumes should contribute more to both food security and sustainable management of natural resources (water, soils) in the next years. A collaborative... more
In the context of climate change, increasing earth population and burst of energy cost, legumes should contribute more to both food security and sustainable management of natural resources (water, soils) in the next years. A collaborative work with research groups in several developing countries during the past 20 years focused on investigation and sampling of local wild legumes (herbs, shrubs and trees) having environmental/agronomic/forestry potential in West Africa and in the Mediterranean region. New symbiotic systems were discovered, resulting in new models for fundamental research, and new applications. This is, for one part, due to their associated microsymbionts, often belonging to unexpected bacterial groups with original physiological / metabolic properties i.e. photosynthesis, freeliving nitrogen fixation, methylothrophy, tolerance to extreme environmental conditions (salinity, aridity, heavy metals, hydrocarbon breakdown), stem nodulation, beneficial associations with no...
Most regions of Saudi Arabia are frequently subjected to high temperature and drought spells which destroy natural vegetation and lead to soil erosion and the advance of sand dunes. The use of legume plants may help to preserve these... more
Most regions of Saudi Arabia are frequently subjected to high temperature and drought spells which destroy natural vegetation and lead to soil erosion and the advance of sand dunes. The use of legume plants may help to preserve these ecosystems and to slow down desertification processes. Legumes produce extensive, deep root systems with a capacity to develop mycorrhizal and rhizobial symbioses facilitating the plant’s nutrition via enhanced soil nutrients absorption and atmospheric nitrogen fixation, respectively. These associations play a vital role in preserving and even restoring the fertility of poor and eroded soils. Research on tripartite associations of Arbuscular mycorrhizal fungi (AMF), rhizobia and legumes is rare in Saudi Arabia. Little is known about the diversity of these beneficial symbioses in Saudi ecosystems and their beneficial role for the sustainable management of range land. We attempted to explore the present status of research on rhizobia and AMF associated w...
Abstract Drylands are highly susceptible to degradation and climate change, which has important ecological and socio-economic consequences worldwide. To halt drylands degradation, plant species selection for restoration is starting to... more
Abstract Drylands are highly susceptible to degradation and climate change, which has important ecological and socio-economic consequences worldwide. To halt drylands degradation, plant species selection for restoration is starting to include also a functional approach, but does not integrate belowground functional traits yet. Therefore we tested the use of mycorrhizal traits to identify native plant species which host guilds of beneficial microbes and therefore enhance multiple soil functions simultaneously – soil multifunctionality. We used a soil organic matter (SOM) gradient (0.9–1.9%) and evaluated the effect of 14 common and abundant native herbaceous plant species (+bare soil) on soil functionality. We measured several soil functions (soil microbial biomass, metabolic quotient, and enzymatic activities – dehydrogenase, β-glucosidase and phosphatase) and built a soil multifunctionality index. Soil multifunctionality was strongly associated with mycorrhizal traits across the analysed SOM gradient. Bare soils and soils under non- or low-mycorrhizal plant species displayed the lower soil functionality (both individual functions and multifunctionality), while soils under Fabaceae species (Medicago truncatula, Astragalus corrugatus and Lotus halophilus) displayed the highest. For each plant species, the highest soil multifunctionality was observed at the SOM-richer site. Soil multifunctionality was strongly associated with all the mycorrhizal traits but mycorrhizal intensity and AMF spores abundance were more correlated with soil multifunctionality than mycorrhizal frequency. Our data show that: i) AM traits can be good indicators of simultaneous multiple soil functions in drylands; and ii) soil multifunctionality in drylands can be improved by management practices promoting SOM accumulation and favouring specific native plant species.
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A collection of rhizobia isolated from Acacia tortilis subsp. raddiana nodules from various arid soils in Tunisia was analyzed for their diversity at both taxonomic and symbiotic levels. The isolates were found to be phenotypically... more
A collection of rhizobia isolated from Acacia tortilis subsp. raddiana nodules from various arid soils in Tunisia was analyzed for their diversity at both taxonomic and symbiotic levels. The isolates were found to be phenotypically diverse. The majority of the isolates tolerated 3% NaCl and grew at 40 °C. Genetic characterization emphasized that most of the strains (42/50) belong to the genus Ensifer , particularly the species Ensifer meliloti , Ensifer garamanticus , and Ensifer numidicus . Symbiotic properties of isolates showed diversity in their capacity to nodulate their host plant and to fix atmospheric nitrogen. The most effective isolates were closely related to E. garamanticus. Nodulation tests showed that 3 strains belonging to Mesorhizobium genus failed to renodulate their host plant, which is surprising for symbiotic rhizobia. Furthermore, our results support the presence of non-nodulating endophytic bacteria belonging to the Acinetobacter genus in legume nodules.
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Seeds of three sorghum (Sorghum bicolor (L.) Moench.) varieties from Southwest Saudi Arabia were used to investigate the potential of osmopriming with polyethylene glycol (PEG 8000) to improve germination performance, seed reserve... more
Seeds of three sorghum (Sorghum bicolor (L.) Moench.) varieties from Southwest Saudi Arabia were used to investigate the potential of osmopriming with polyethylene glycol (PEG 8000) to improve germination performance, seed reserve utilization and early seedling growth and drought stress tolerance. The primed (PS) and unprimed (UPS) seeds of the three sorghum varieties were germinated for 8 days under increasing PEG-induced osmotic stress. The treatments were arranged in a completely randomized design, in a factorial arrangement, with three sorghum cultivars (‘Zaydia’, ‘Shahbi’ and ‘Ahmar’) and four osmotic potentials (0.0; -0.4; -0.8 and -1.2 MPa) with four replicates of 50 seeds each. The results showed that drought stress affected seed germination and seedling emergence and establishment, but increased the activity of the antioxidant enzyme catalase (CAT). The strongest inhibition of germination and growth occurred at the highest PEG concentration and a significant difference was ...
Arbuscular mycorrhizal fungi (AMF) are determinant for the performance of plant communities and for the functionality of terrestrial ecosystems. In natural ecosystems, grazing can have a major impact on mycorrhizal fungi and consequently... more
Arbuscular mycorrhizal fungi (AMF) are determinant for the performance of plant communities and for the functionality of terrestrial ecosystems. In natural ecosystems, grazing can have a major impact on mycorrhizal fungi and consequently on plant growth. The objective of this study was to evaluate the statements referred above in Mediterranean arid areas in Tunisia. Root samples and rhizosphere soils of five dominant herbaceous plants were studied at six distinct arid sites differing on soil proprieties and grazing intensity. At each site, chemical and dynamic properties of the soil were characterized as well as the AMF colonization intensity and the soil functionality. Results showed that the mycorrhizal frequency and intensity and spore density, varied between plants in the same site and, for each plant, between sites and evidenced a positive effect of mycorrhized plants on soil microbial activity. Grazing and soil properties strongly affected AMF composition and the soil microbia...
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For a long time, the people of Saudi Arabia have been using medicinal plants (MPs) as conventional medicine to heal diverse human and livestock diseases. The present work is the first study on ethnobotanical uses of 124 MPs species used... more
For a long time, the people of Saudi Arabia have been using medicinal plants (MPs) as conventional medicine to heal diverse human and livestock diseases. The present work is the first study on ethnobotanical uses of 124 MPs species used by the local tribal communities of Jazan province in the Southwest of Saudi Arabia. Ethnobotanical data were collected by interviewing 174 local informants using semistructured interviews. Informants of different ages, from several settlements belonging to several tribal communities, were interviewed. It is worth noticing that the age of informants and their knowledge of MPs were positively correlated, whereas the educational level and MP knowledge of participants were negatively correlated. To find out if there was agreement in the use of certain plants in the treatment of given ailments, we used Informant Consensus Factor (ICF). To determine the most frequently used plant species for treating a particular ailment category by local people we used th...
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Drinking water quality plays a remarkable role in human infections and diseases. This study used polymerase chain reaction (PCR) techniques to detect bacterial pathogens. In addition, a physicochemical analysis was performed on drinking... more
Drinking water quality plays a remarkable role in human infections and diseases. This study used polymerase chain reaction (PCR) techniques to detect bacterial pathogens. In addition, a physicochemical analysis was performed on drinking water samples from several sources. A total of 123 drinking water samples were collected from different areas in the Jazan region in Saudi Arabia: ground water (40 samples), bottled water (15 samples), tap water (52 samples), and water purification shops (16 samples). To isolate the bacterial pathogens, the water samples were spread on Nutrient and MacConkey agar media, and the grown pathogens were then identified by the 16S ribosomal RNA technique. In 87 (70.7%) of the 123 drinking water samples, there was no pathogen growth on the two-culture medium. However, 36 (29.3%) of the samples were found to be contaminated with bacteria. The physicochemical analysis indicated that the water samples were within the Saudi drinking water standards. The bacteri...
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Mycorrhizal symbioses are considered indicators of ecosystem biodiversity. However, their diversity and relevance in arid and semi-arid ecosystems are poorly understood. This study addressed this subject, the main objective being to... more
Mycorrhizal symbioses are considered indicators of ecosystem biodiversity. However, their diversity and relevance in arid and semi-arid ecosystems are poorly understood. This study addressed this subject, the main objective being to evaluate arbuscular mycorrhizal fungi (AMF) diversity and heterogeneity in a semi-arid region. Samples of bulk and rhizosphere soil and fine roots of Medicago truncatula were collected at four different sites with the same aridity index (6.1), in Bou-Hedma National Park, Tunisia, a semi-arid ecosystem. AMF taxa were assessed by 454- pyrosequencing and identified by BLAST matching of operational taxonomic units (OTUs) against the MaarjAM database, targeting AMF SSU rRNA gene diversity. Roots were the hotspots of AMF diversity (107 OTUs out of a total of 138). Of the 138 OTUs, 113 found correspondence in the MaarjAM database, with 32 AMF virtual taxa (VTX),19 Site-exclusive (SE) and 13 common to at least two sites (Non-site exclusive, NSE); the remaining 2...
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Arbuscular mycorrhizal fungi (AMF) constitute a key functional group of soil biota that can greatly contribute to crop productivity and ecosystem sustainability. They improve nutrient uptake and enhance the ability of plants to cope with... more
Arbuscular mycorrhizal fungi (AMF) constitute a key functional group of soil biota that can greatly contribute to crop productivity and ecosystem sustainability. They improve nutrient uptake and enhance the ability of plants to cope with abiotic stresses. The presence of AMF in coffee (Coffea arabica L.) plant roots have been reported in several locations but not in Saudi Arabia despite the fact that coffee has been in cultivation here since ancient times. The objective of the present study was to investigate the diversity of AMF communities colonizing the roots of coffee trees growing in two sites of Fifa Mountains (south-west Saudi Arabia): site 1 at 700 m altitude and site 2 at 1400 m. The AMF large subunit rDNA regions (LSU) were subjected to nested PCR, cloning, sequencing, and phylogenetic analysis. Microscopic observations indicated higher mycorrhizal intensity (24.3%) and spore density (256 spores/100 g of soil) in site 2 (higher altitude). Phylogenetic analysis revealed 10 phylotypes, six belonging to the family Glomeraceae, two to Claroideoglomercea, one to Acaulosporaceae and one to Gigasporaceae family. Glomus was the dominant genus at both sites and the genus Gigaspora was detected only at site 2. This is the first study reporting the presence of AMF in coffee roots and the composition of this particular mycorrhizal community in Saudi Arabia.
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Fifty seven bacterial isolates from root nodules of two spontaneous legumes (Astragalus corrugatus and Hippocrepis areolata) growing in the arid areas of Tunisia were characterized by phenotypic features, 16S rDNA PCR-RFLP and 16S rRNA... more
Fifty seven bacterial isolates from root nodules of two spontaneous legumes (Astragalus corrugatus and Hippocrepis areolata) growing in the arid areas of Tunisia were characterized by phenotypic features, 16S rDNA PCR-RFLP and 16S rRNA gene sequencing. Phenotypically, our results indicate that A. corrugatus and H. areolata isolates showed heterogenic responses to the different phenotypic features. All isolates were acid producers, fast growers and all of them used different compounds as sole carbon and nitrogen source. The majority of isolate grew at pHs between 6 and 9, at temperatures up to 40°C and tolerated 3% NaCl concentrations. Phylogenetically, the new isolates were affiliated to four genera Sinorhizobium, Rhizobium, Mesorhizobium and Agrobacterium. About 73% of the isolates were species within the genera Sinorhizobium and Rhizobium. The isolates which failed to nodulate their host plants of origin were associated to Agrobacterium genus (three isolates).
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ABSTRACT There is growing interest in assessing soil quality using microbial properties in desertified areas. A study was conducted in arid soils subjected to desertification in the south of Tunisia to illustrate the effects of dominating... more
ABSTRACT There is growing interest in assessing soil quality using microbial properties in desertified areas. A study was conducted in arid soils subjected to desertification in the south of Tunisia to illustrate the effects of dominating steppes of Stipa tenacissima and Anthyllis sericea subsp. henoniana on soil chemical, microbial, and biochemical properties. Soil samples were collected beneath the canopy of S. tenacissima, A. sericea subsp. henoniana, and open areas in the rainy and dry seasons.These steppes showed higher values of soil organic carbon content (Corg). Microbial biomass carbon (Cmic) was also greater under steppes and reached 289 μg C g−1 soil under Anthyllis canopies. Studied enzyme activities (dehydrogenase, phosphatase and β-glucosidase) increased greatly beneath steppes showing dehydrogenase activity of 159 μg INTF g−1 soil d−1, while it did not reach 36 μg INTF g−1 soil d−1 in open areas. Conversely, lower values of C/N ratio and metabolic quotient (qCO2), particularly in the vicinity of A. sericea subsp. henoniana.The environmental conditions significantly affected studied properties: the soil organic carbon, microbial biomass, and enzyme activities were reduced in dry season, while C/N ratio and qCO2 were higher.Our results suggest the importance of vegetation cover in regulating soil microbial processes in arid degraded areas and that the wet season may play an important role in driving seasonal changes in microbial biomass and activity.
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Legumes play a critical role in natural ecosystems, agriculture, and agroforestry, where their ability to fix nitrogen (N) in symbiosis makes them excellent colonizers of low-N environments, and hence an economic and environment-friendly... more
Legumes play a critical role in natural ecosystems, agriculture, and agroforestry, where their ability to fix nitrogen (N) in symbiosis makes them excellent colonizers of low-N environments, and hence an economic and environment-friendly crop, pasture, and herb species. Few reports exist on natural nodulation of wild legumes. The natural nodulation resource of five pastoral legumes, among which three Loteae (Lotus
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Genista saharae, indigenous of Sahara, is a spontaneous shrub that plays an important ecological role for the preservation and fertility of poor and eroded soils. This legume has not been examined for its root nodule bacteria. The... more
Genista saharae, indigenous of Sahara, is a spontaneous shrub that plays an important ecological role for the preservation and fertility of poor and eroded soils. This legume has not been examined for its root nodule bacteria. The taxonomic diversity of bacteria from root nodules of G. saharae growing in the infra-arid region of Tunisia was investigated. A total of 28 bacterial strains isolated from root nodules of G. saharae grown in Tunisian soil were characterized using a polyphasic approach including phenotypic characteristics, PCR-RFLP of 16S rDNA and 16S rRNA gene sequencing. It was found that new isolates are diverse and affiliated to Ensifer (75%), Rhizobium (10%) and Phyllobacterium (15%). The Phyllobacterium isolates lacked the capacity for nodule formation on this plant. Genista saharae formed nodules with diverse rhizobia in Tunisian soils. Furthermore, our results support the presence of non-nodulating commensal strains (Phyllobacterium) in legumes nodule. This study is the first report on the characterization of G. saharae microsymbionts in Tunisia.
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A bacterial strain, designated PW21T, was isolated from root nodules of Prosopis farcta in Tunisia. Phylogenetic analysis based on 16S rRNA gene sequences placed the isolate into the genus Paenibacillus, with its closest relatives being... more
A bacterial strain, designated PW21T, was isolated from root nodules of Prosopis farcta in Tunisia. Phylogenetic analysis based on 16S rRNA gene sequences placed the isolate into the genus Paenibacillus, with its closest relatives being Paenibacillus glycanilyticus DS-1T and Paenibacillus castaneae Ch-32T with identity values of 96.9 %. DNA–DNA hybridization measurements showed values of less than 25 % with respect to these two species. The isolate was a Gram-variable, motile and sporulating rod. Catalase activity was positive and oxidase activity was weakly positive. Aesculin, CM-cellulose, xylan and starch were hydrolysed but casein and gelatin were not. Acetoin production was weakly positive and nitrate reduction was negative. Urease production was negative. Growth was supported by many carbohydrates and organic acids as carbon sources. MK-7 was the predominant menaquinone and anteiso-C15 : 0, iso-C16 : 0 and iso-C15 : 0 were the major fatty acids. Major polar lipids were diphosp...
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Forty-two bacterial isolates from root nodules of Argyrolobium uniflorum growing in the arid areas of Tunisia were characterized by phenotypic features, RFLP, and sequencing of PCR-amplified 16S rRNA genes. The isolates were found to be... more
Forty-two bacterial isolates from root nodules of Argyrolobium uniflorum growing in the arid areas of Tunisia were characterized by phenotypic features, RFLP, and sequencing of PCR-amplified 16S rRNA genes. The isolates were found to be phenotypically diverse. The majority of the isolates tolerated 3% NaCl and grew at temperatures up to 40 °C. Phylogenetically, the new isolates were grouped in the genera Sinorhizobium (27), Rhizobium (13), and Agrobacterium (2). Except for the 2 Agrobacterium isolates, all strains induced nodulation on Argyrolobium uniflorum, but the number of nodules and nitrogen fixation efficiency varied among them. Sinorhizobium sp. strains STM 4034, STM 4036, and STM 4039, forming the most effective symbiosis, are potential candidates for inoculants in revegetalisation programs.
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ABSTRACT There is growing interest in assessing soil quality using microbial properties in desertified areas. A study was conducted in arid soils subjected to desertification in the south of Tunisia to illustrate the effects of dominating... more
ABSTRACT There is growing interest in assessing soil quality using microbial properties in desertified areas. A study was conducted in arid soils subjected to desertification in the south of Tunisia to illustrate the effects of dominating steppes of Stipa tenacissima and Anthyllis sericea subsp. henoniana on soil chemical, microbial, and biochemical properties. Soil samples were collected beneath the canopy of S. tenacissima, A. sericea subsp. henoniana, and open areas in the rainy and dry seasons.These steppes showed higher values of soil organic carbon content (Corg). Microbial biomass carbon (Cmic) was also greater under steppes and reached 289 μg C g−1 soil under Anthyllis canopies. Studied enzyme activities (dehydrogenase, phosphatase and β-glucosidase) increased greatly beneath steppes showing dehydrogenase activity of 159 μg INTF g−1 soil d−1, while it did not reach 36 μg INTF g−1 soil d−1 in open areas. Conversely, lower values of C/N ratio and metabolic quotient (qCO2), particularly in the vicinity of A. sericea subsp. henoniana.The environmental conditions significantly affected studied properties: the soil organic carbon, microbial biomass, and enzyme activities were reduced in dry season, while C/N ratio and qCO2 were higher.Our results suggest the importance of vegetation cover in regulating soil microbial processes in arid degraded areas and that the wet season may play an important role in driving seasonal changes in microbial biomass and activity.
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ABSTRACT Fifteen bacterial isolates, representatives of different 16S rRNA-RFLP genomogroups which were isolated from root nodules of Lotus creticus and L. pusillus growing in the arid areas of Tunisia were characterized by phenotypic... more
ABSTRACT Fifteen bacterial isolates, representatives of different 16S rRNA-RFLP genomogroups which were isolated from root nodules of Lotus creticus and L. pusillus growing in the arid areas of Tunisia were characterized by phenotypic features and 16S rDNA sequences. Phenotypically, all isolates are fast growers with the ability to grow at a pH between 5.5 and 9. Most of the tested isolates tolerate NaCl concentrations from 1.39 to 3.48 %. Phylogenetically, the studied isolates are affiliated into the genera: Sinorhizobium (5 strains), Rhizobium (2 strains), and Mesorhizobium (4 strains). The 16S rDNA sequences of Tunisian Lotus sp. nodule isolates: LAC7511, LAC733, and Mesorhizobium alhagi (Alhagi sparsifolia symbiont) shared 100 % identical nucleotides similar to the 16S rDNA sequences of LAC831, LAC814 and Mesorhizobium temperatum CCNWSX0012-2 (Astragalus adsurgens symbiont). Non-nodulating bacteria, considered as endophytes of Lotus sp. nodules, were also found in our studies and they were classified into the genera: Phyllobacterium (2 strains), Starkeya (1 strain) and Pseudomonas (1 strain). Except for these four endophytic Lotus sp. bacteria, all other strains under investigation induce nodules on Lotus sp., but they differ in the number of induced root nodules and the effectiveness of atmospheric nitrogen fixation. The Sinorhizobium sp., Mesohizobium sp. and Lotus sp. nodule isolates, forming the most effective symbiosis with the plant host, are potential candidates for inoculants in revegetation programs.